Should we eat more fat?

People usually treat fat as the most harmful thing to a healthy diet. WHO suggests that the total fat intake of an adults should be less than 30% of the total energy intake. The energy intake from saturated fat should be less than 10%. Over intake of fat contribute to unhealthy weight gain. Over intake of saturated fat contribute to several chronic diseases.

A recent study on the associations of fats and carbohydrate intake with cardiovascular disease and mortality makes some of my friends hesitate to continue their low fat diet. The study is a prospective cohort study on people from 18 countries.

In the conclusion part of this study, authors suggests that the guideline of healthy diet should be reconsidered referencing this study as well as other studies which have similar results with this one. First of all, this study is a cohort study. In the study of epidemiology, cohort study usually just give the possibility of an association of diseases with exposures. In order to find the causal association between high fat intake and lower mortality, the randomised controlled trial is the most valid way (the golden standard). The real world evidence study was also been used recent years.

Comments from other scientists

After the publication of this study, there were comments from another group of scientists been published on the same journal. They think this study did challenge the traditional definition of a healthy diet in terms of fat intake. However, there are questions remain which need further study.

First of all, the fat intake of this study was mostly source from animal products (dairy and meat). Different kinds of fat and protein in this study are all associated with better survival. It can be the fact that meat and dairy intake is associated with lower mortality. However, in the common guideline of healthy diet, people are encouraged to have higher white meat and diary intake.

Secondly, animal products are rich sources of zinc, bioavailable iron, vitamin K2, and vitamin B12 which means higher fat intake usually come with this important nutrition. The lower mortality might due to the richness of this nutrition in animal products. Which means the lower mortality observed in this study was not necessary due to higher fat intake.

Thirdly, the population of this study was from Europe and North America. People in these area have gain the information of healthy diet and other healthy lifestyles for many years. The association between fat intake and mortality might be confounded by the conscientiousness for other healthy behaviours. Which means the knowledge of other healthy behaviours contribute to both the total fat intake (fishes and nuts rich in monounsaturated fat) and lower mortality.

What should we do?

Before further studies are completed, it seems too early to change our mindset for a healthy diet. The recommendations from guideline like Australian Dietary Guidelines are still trust worthy. We can leave the debate for sugar VS fat which is more harmful aside for now, and have both of them been controlled in a reasonable range.